The source of the helium visible lines in η Carinae

We assume that the helium-I lines emitted by the massive binary system eta Carinae are formed in the acceleration zone of the lessmassive secondary star. We calculate the Doppler shift of the lines as a function of orbital phase and of several parameters of the binary system. We find that a good fit is obtained if the helium lines are formed in the region where the secondary wind speed is nu(zone) = 430 km s(-1). The acceptable binary eccentricity is in the range 0.90 less than or similar to e less than or similar to 0.95, and the inclination angle (the angle between a line perpendicular to the orbital plane and the line of sight) is in the range 40 degrees less than or similar to i less than or similar to 55 degrees. Lower values of e require higher values of i, and vice versa. The binary system is oriented such that the secondary star is in our direction (closer to us) during periastron passage. The orbital motion can account in part to the Doppler shift of the peak in X-ray emission. (c) 2007 Elsevier B.V. All rights reserved.